Paper manufacture



Patented ar. 1, 1932 GLYDE A. BENSON, 0F PORTLAND, MAINE, ASSIGNOR TO RAJPFOLD PROUES'S CORPORA- TION', OF ANDOVER, MASSACHUSETTS, A CORPORATION OF MASSACHUSETTS PAPER MANUFACTURE Ho Drawing.

In the manufacture of certain grades of paper, such as magazine and book papers, it is the practice to incorporate a loading or filling material into the paper, together with a certain amount of sizing material, in order to produce a product having the desired weight, opacity, printing surface, and'water resistance. The loading and sizing materials are incorporated into the paper pulp in the beater engine, and the sizing material precipitated before the pulp is run off into paper on the paper machine. The precipitation of the sizing material is usually effected by an acidic reagent, suchv as acid salts of the trivalent and divalent metals, alum generally being used where the sizing material employed is rosin size and discoloration of the resulting paper is to be avoided.

Where acidic reagents such as alum have been used to efiect the precipitation of sizing material in the presence of loading material, it has heretofore been necessary to employ loading materials which are inert with respect to an acidic reagent, as otherwise reaction isefi'ected upon the loading materials, this not only seriously hindering the sizing operation, but sometimes resulting in reaction products which interfere with the production of good grade paper. For instance, if calcium carbonate is incorporated together with rosin size into paper pulp in the beater engine, and alum added to efiect the precipitation of the size, it is found that a selective reaction takes place upon the calcium carbonate,

, liberating carbon dioxide and producing calpacity of a mill would be greatly decreased,

for the reaction between calcium carbonate and alum requires considerable time in the presence of fibrous material'and size. More over, the carbon dioxide liberated during the Application filed November 30, 1927. Serial Ito. 236,885.

reaction produces violent foaming in the heater, and elfervescence in the pulp tends to "persist even to the paper machine, the bubbles of carbon dioxide being likely to cause imperfections in the finished sheet of paper. Furthermore, the increased expense of alum becomes a factor of considerable importance, particularly where a large amount of calcium carbonate is used. I

It might be reasoned, off-hand, that if the size were precipitated on the pulp before incorporating the calcium carbonate, reaction upon the calcium carbonate would be avoided, but research work evidences the fallacy of such reasoning. (See, for example, Sutermeisters Chemistry of Pulp and Paper Making, 1920, page 300.) Thus, after the precipitation of size with alum, an acidic, in fact a distinctly acidic condition, prevails in the pulp. Upon the addition of the desired amount of calcium carbonate to the pulp, reaction immediately takes place upon the calcium carbonate, carbon dioxide being evolved and the precipitated size being degraded or decomposed to such an extent that its sizing.

reaction takes place between the calcium carbonate and both the free acid and precipitated size, the reaction of the calcium carbonate with these materials proceeding in step-bystep fashion or simultaneously. If suflicient calcium carbonate has been added to combine with all the reactable materials, analkaline condition prevails in the pulp after the reaction has ceased.

In accordance with the present invention, loading materials, such as calcium carbonate, which react with ,acid reagents are rendered passive to such reagents. This may be accomplished by treating the loading material with emulsified thermoplastic material, such as paraflin, which is substantially inert with respect to both the loading material and the acidic reagent. My invention, may therefore, be applied to great advantage when it is desired to incorporate loading materials, such as calcium carbonate, which react with acidic reagents, into paper pulp to which an acidic reagent is added, for by the use of suitable thermoplastic materials in emulsified condition, together with the loading material, reaction between the acidic reagent and the loading materials is prevented. The emulsified thermoplastic material further serves as an g excellent sizing or waterproofing agent, and hence may be used alone or together with rosin size to render the resulting paper water-resistant. Only a relatively small amount of emulsified thermoplastic material is necessary q to prevent reaction between the loading material and acid reagent, for instance 1% and even less of emulsified paraffin (based on dry he use of calcium carbonate in the produc tion of sized papers in accordance with the present invention is of considerable commercial importance, as calcium carbonate is produced in large quantities as a waste product in paper mills employing the soda and kraztt ac processes of producing pulp. in these procasses, the inorganic content of the spent cool:- ing liquor is smelted to produce a sodium carbonate-containing smelt, which is dissolved to form a smelt solution. The smelt solution is then treated with lime to convert the sodium carbonate into caustic soda, this being acconb panied by the precipitation of calcium carbonate or so-called lime sludge, which is separated from the causticized solution to be used for the production of pulp. The calcium carbonate sludge thus obtained is sometimes dumped near the mill, and is often discharged into natural waterways, constituting a nuisance. My invention makes this waste product available for use as a loading material in the manufacture of sized papers, as it requires little expense to condition it for this purpose. lit possesses the great advantage over china clay, which is a relatively expensive material customarily used in loading sized papers because of its inert character, in that with a given amount of sizing material it yields a finished paper of much superior water resistance.

1 The emulsion employed for rendering the calcium carbonate passive to acidic reagents may-be prepared from various thermoplastic materials,,or mixtures of such materials, e. g.,

waxes such as parafin, Montan or carnauba,

or even asphalts. Where discoloration of the finished paper is to be avoided. 1 preferably employ parafiin, together with a small amount of Mont-an wax, if desired. llhe parafiin may be emulsified as the internal phase by the use :.of various emulsifying or dispersing agents,

for instance by the employment of a solution of sodium silicate or by a solution oil soap such as rosin size, or by a mixture of both solutions. Inasmuch as results secured indicate that rosin size when used alone and precipitated on the pulp with alum, without the presence of calcium carbonate, gives a better-sized paper than when a corresponding amount of parafin emulsified in sodium silicate solution is used alone under the same conditions, I preferably employ an emulsion containing both emulsified paraffin and rosin size, the emulsified parafin rendering the cal cium carbonate passive and also serving to size the pulp and the rosin size, at the same time serving to impart its superior sizing efiect when precipitated. One emulsion comprising para-fun and rosin size which has been used extensively in the commercial applica- 'tion of my invention is prepared about as follows. Two parts of soda ash is added to 56 parts of water, solution of the soda ash being hastened, if desired, by heating the water. To this solution is added 12 parts of rosin, the mixture being suitably heated and agitated until the saponifica-tion reaction between the rosin and soda ash to produce rosin s ze is complete, this being manifest by almost complete cessation of foaming. To this resulting rosin size, is added 8 parts of parafin, the parafin melting in the hot size and becoming emulsified therein as agitation is continued. After thorough agitation of this mixture, 1 part of Montan wax is added during agitation, and the mass is further agitated until the Montan wax has completely melted and emulsified, whereupon the mass is cooled to approximately the melting point of the paraffin and passed through a colloid mill, which ensures substantially complete emulsification of both the parafin and Montan wax.

The calcium carbonate to be used as a load ing material may be incorporated into the emulsion at a suitable stage during its preparation, for instance before it is passed through the colloid mill, or it may be incorporated into the paper pulp in the beater engine independently of the emulsion. If the calcium carbonate is the lime sludge obtained as a waste product from the soda or krait process of producing pulp, it may be readily conditioned for. use as a loading material by removing any dirt or coarse material contained therein, and grinding to ensure a product substantially all of which passes through a 200-mesh sieve. If desired, any free lime present therein may be carbonated, and any sodium salts contained therein removed by washing.

A procedure whih may be employed in loading and sizing pulp especially intended. for the manufacture of magazine and book papers may be substantially as follows. Six

hundred pounds of sulphite pulp (air-dry) and 400 pounds of soda pulp-"(air=dry) are added to the beater engine, together with suficient water to ensure circulation of the mass. Three hundred and seventy-five pounds of finely divided calcium carbonate (bone-dry) is then added in the form of a uniform aqueous paste or sludge, and is thoroughly disseminated throughout the mass of pulp by the operation of the engine. Seyenty-eight pounds of emulsion prepared as previously described and containing parafiin and Montan wax emulsified in rosin size solution, is then added to the engine, whereupon the pulp may be beaten to the slowness desired for pa'permaking. After beating for about, say, 15 minutes, (or longer, if desired), a

solution containing 30 pounds of alum is added to effect a precipitation of the rosin size, whereupon heating is continued for awhile and a solution containing 30 pounds of alum is again added to the engine, this ensuring precipitation of substantially all the size and producing a pH Value of 7.5 in the pulp, which indicates slight alkalinity. The pulp may then be jordanned, if desired, diluted to papermaking consistency, and run oil into any usual paper on a papermaking machine, and calendered, if desired. The resulting dried paper is water-resistant and contains about 27.1% calcium carbonate, and is especially suitable for use as book and magazine paper. 1

It is to be understood that the foregoing example is illustrative only, and that the various raw materials and proportions therein recited may be varied greatly, depending upon the characteristics of the product which it is desired to produce. Furthermore, a

pulp loaded and sized as herein described may be employed in the production of moulded pulp articles which do not require the use of a paper machine.

I am aware of the fact that it has been proposed to use emulsions of various thermoplastic materials, such as paraffin, or asphalt dispersed in water with colloidal clay as a dispersing agent, to size paper pulp in the beater engine, andI do not claim this step per se;

but, so far as I am aware, I am the first to render inert or inactive a loading material, such as calcium carbonate or waste lime sludge, capable of reacting with a precipitat ing agent such as alum, by the employment of an inert thermoplastic, and thus to secure the benefits and advantages which I have hereinbefore pointed out.

Having thus described certain embodiments of my invention, it is evident that change and modification might be made therein without departing from the spirit or scope of invention as defined in the appended claims.

What I claim is:

1. A method of rendering finely divided calcium carbonate passive to the action of alum solution, which comprises treating such 3. A method of loading and sizing paper,

which comprises incor orating into paper pulp finely divided ca cium carbonate together with a paraflin-rosin size emulsion, adding alum to precipitate the size, and running the pulp off on a paper machine.

4:. A.method of loading and sizing paper, which comprises incorporating into paper pulp finely divided calcium carbonate together with a rosinsize emulsion of paraflin and Montan wax, adding alum to ensure precipitation of the size but without producing an acidic condition in the pulp, and running the pulp off on a paper machine.

5. A loaded and well-sized paper containing calcium carbonate, rosin size, and a thermoplastic material inert with respect to said calcium carbonate.

6. A loaded and well-sized paper containing calcium carbonate, rosin size, and paraflin.

A method of sizing and loading paper pulp involving the use of acidic precipitating agents and loadin materials which react with such agents, which comprises incorporating such loading materials into the pulp together with a rosin size emulsion of thermoplastic material which renders the loading materials passive to such agents, and then adding such agents to efi'ect a precipitation of the size and thermoplastic material on the fibers.

In testimony whereof I have aflixed my signature.

CLYDE A. BENSON. 

